The disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
Certain aspects of the invention relate to wireless communications systems. Other aspects of the invention relate to active radiator subsystems which serve as building blocks for cellular base stations. Other aspects of the invention relate to systems and methods for implementing cellular base station systems.
Cellular wireless communications systems provide users with wireless access to voice and data networks throughout a given geographic serving area. Transmit/receive base stations, dispersed throughout the serving area communicate with the users"" mobile stations. Usually, each base station serves a certain portion of the serving area, such as a xe2x80x9ccell.xe2x80x9d As a user moves from one cell into an adjacent cell, the call is handed off from the base station assigned to the first cell to the base station assigned to the adjacent cell. There are many types of cellular systems, including advanced mobile phone system (AMPS), code-division multiple access (CDMA), Digital AMPS, global system for mobile communications (GSM), nordic mobile telephone (NMT), total access communications system (TACS), and personal communication systems (PCS). PCS cellular systems may utilize such technologies as DCS 1800, PCS 1900, GSM, personal digital cellular (PDC), IS-661, IS-136, and IS-95, technologies, among others.
The base station covers a given geographical coverage area and connects and controls any mobile station within its coverage area. The base stations serve as a xe2x80x9ccell sitesxe2x80x9d for their respective cells. A cell site typically comprises at least one transmit antenna and at least one receive antenna. Multiple transmission signals are typically connected to the transmitting antenna after being combined with the use of a combiner.
A given cell site radiates power at a controlled level and comprises an antenna positioned at a height sufficient to cover the cell area. This permits frequency reuse of the same channels in non-adjacent cells within the same cellular geographic serving area, while mitigating co-channel interference. A well-coordinated frequency reuse plan enables a large number of simultaneous calls to be handled throughout the cellular geographic serving area. To further increase the traffic capacity that can be handled within a given service area, congested cells can be subdivided into smaller cells, wherein each smaller cell may be provided with its own base station. These smaller cells then use lower transmitter power and antennas with a lower height, thus permitting a greater frequency reuse. These subdivided cells can be split still further for greater frequency reuse. Such cell splitting can be employed with the use of directional antennas, for example, to mitigate interference brought about by increased frequency reuse.
Because mobile stations are likely to be in motion, it is difficult to control the line of sight (LOS) between a given base station and the mobile station. Such motion changes the path characteristics, causing multi-path propagation. Multi-path propagation results in such undesirable effects as multi-path fading and dispersion.
Diversity techniques are used to combat these effects. Some types of diversity used to reduce the effects of fading and to mitigate dispersion include frequency diversity, spatial diversity, time diversity, angle diversity, and polarization diversity. Spatial diversity involves physically separating the antennas by a defined physical separation, which can be either horizontal or vertical.
Polarization diversity involves utilizing two different antenna elements that are polarized in different (e.g., orthogonal) planes. One advantage polarization diversity presents in a mobile communications system is a reduced number of antennas required for an installation.
Time diversity transmits the information at different times, while frequency diversity transmits the information content at different frequencies. Angle diversity varies the angle of arrival of the signal.
There are a number of different access methods used to facilitate full-duplex communication between base stations and mobile stations. They include frequency-division multiple access (FDMA), time-division multiple access (TDMA), and code division multiple access (CDMA). Typically, with each of these access methods, a radio bandwidth segment is allotted, and a portion of the bandwidth is assigned for transmission from a cell site to the mobile stations, (the xe2x80x9cforward linkxe2x80x9d), while another portion is assigned for communication from the mobile station to the cell site (the xe2x80x9creverse linkxe2x80x9d). The allotted bandwidth segment is placed at a certain position within the frequency spectrum with the use of a carrier signal. Some systems utilize multiple carriers, such as the multicarrier operation of a CDMA network, which maximizes the capacity of the network for the allocated band. The cellular band allows for a maximum of 8 CDMA carriers, while the A, B, C bands allow for 11 carriers each, and the G, E, F bands allow for three carriers each.
FIG. 1 shows a typical wireless communication site for cellular and PSC communications. The illustrated site comprises, among other elements not specifically shown, batteries 12, a control bay 14, a receive bay 16, a transmit bay 18, and a filter bay 20. Cables connecting filter bay 20 to antenna element(s) 26 are passed through a cable tray 22. The antenna element(s) assembly is mounted at the top of a tower/mounting structure 24.
Communication sites such as the one shown in FIG. 1 are more frequently incorporating directional antenna arrangements rather than omni directional antennas. These sites break down omni 360xc2x0 cells into smaller angular range sectors, such as 120xc2x0 sectors. These directional systems help to reduce interference due to channel overlap and to increase the transmit and receive distance ranges of the base station. Accordingly, the cells can cover a larger area, and communication signals within each cell are stronger. By way of example, U.S. Pat. Nos. 5,889,494 (Reudink et al.), U.S. Pat. No. 5,565,873 (Dean), and U.S. Pat. No. 5,666,123 (Chrystie) each disclose base station systems utilizing multi-beam directional antenna array arrangements.
The antenna arrangements provided at a given communications site will preferably occupy the least amount of space, and be mounted so as to create the least amount of intrusion and nuisance. For example, if the antenna arrangement is mounted at the top of a building, it may block the view of occupants of adjacent buildings. In addition, it is preferred that the antenna arrangement be configured so that it can be easily mounted to structures of various types. The shape, size, and configuration of the antenna arrangement will determine how and whether the arrangement can be mounted to a particular structure. Moreover, because these arrangements are within plain view in many environments, such as in urban environments, it is important that the arrangements be aesthetically pleasant.
In addition, the communications site should preferably be designed so that it utilizes the least amount of power, yet accommodates the full EIRP/range requirements for a given coverage area (e.g., cell or sector). Minimizing power use and reducing transmission losses provide significant advantages to a cellular service provider, such as increasing coverage and improving the quality of communication.
The cost and inconvenience associated with installing, replacing, and upgrading communication sites should not be ignored. Existing cellular base station systems need improvements to make them more easily scalable, customizable, and upgradable.
There is a need for novel and beneficial ways of addressing these issues, and others, in the implementation of cellular base station systems, and more particularly in the implementation of communication sites serving limited coverage areas, such as cells and sectors.
The present invention is provided to improve upon wireless communications systems. Certain aspects of the present invention are provided to facilitate the implementation and modification of cellular base station systems. In order to achieve these ends, one or more aspects of the present invention may be followed in order to bring about one or more specific objects and advantages, such as those noted below.
One object of the present invention is to provide improvements relating to antenna arrangements in communication sites for cellular wireless communication systems. A further object of the present invention is to provide certain antenna and active radiator subunit arrangements for cellular wireless communications sites. Such arrangements preferably address a number of issues pertaining to cellular wireless communications. Those issues include multipath fading and constraints in the amount of space a given antenna arrangement shall occupy. They also include the aesthetic nature of the antenna arrangement, transmission loss and power usage concerns, the range of coverage provided by a given antenna arrangement, and the cost of manufacturing and assembling various portions of the cellular cell site system. Novel and beneficial features are also desirable to facilitate the scalability, customizability, and reuse of components of a communications site, as well as the upgrading of the communications site.
The present invention, therefore, may be directed to certain antenna arrangements, active radiator units which may be used to form such antenna arrangements, and various subcomponents of such antenna arrangements and active radiator units. Certain aspects of the present invention are also directed to systems and methods, and portions thereof, for assembling and arranging antenna elements, active radiator units, and subcomponents of such antenna arrangements and active radiator units. Still further aspects of the present invention are directed to systems, methods, and portions thereof, for controlling the operation of one or more aspects of a communications site, particularly the active radiator units within a given antenna arrangement.